The present invention relates to a power frame saw of the type having a machine frame and workpiece clamping jaws, as described in U.S. Pat. No. 3,492,902.
Such a known machine permits a setting of the charging piston stroke and the cutting pressure valve in dependence upon the inclination of the pivotably articulated saw parts, for thickwalled workpiece cross sections. For this purpose, stated briefly, the stroke of the charging piston and the setting of the cutting pressure valve are varied with the aid of a control cam in dependence upon the inclination angle of the pivotable saw parts. This however requires that for the practically occurring workpiece cross sections a corresponding number of interchangeable control cams must be kept available for installation. Thus, firstly, the purchase costs are high and, secondly, operating errors are likely. Therefore, the need exits for a simpler way of taking account of different workpiece cross sections, especially for the cases where simpler automatic saws are used and where relatively small numbers of pieces are to be cut from one cross section.
Moreover, in the known power frame saw the charging piston, irrespective of the size of the workpiece cross section, always carries out the stroke which is possible due to its actuation apparatus. This stroke suffices for small cross sections for economical sawing, while for large workpiece cross section, on account of the cutting resistance, it has the consequence that a more or less large part of the pressure medium delivered in each case by the charging piston is forced away again by way of the cutting pressure valve during the working stroke. Thus in practice pressure medium is delivered unnecessarily with every saw frame stroke, which signifies an unnecessary power consumption and a considerable heating of the hydraulic pressure medium. Furthermore overcontrolling is possible in that, during the return stroke, when the charging piston is delivering pressure medium for the application of the saw blade, the saw blade is applied to the workpiece too early.